The present invention is directed to toners suitable for use in electrostatic imaging processes. More specifically, the present invention is directed to toner compositions that can be used in processes such as electrography, electrophotography, ionography, or the like, including processes wherein the toner particles are triboelectrically charged and processes wherein the toner particles are charged by a nonmagnetic inductive charging process. One embodiment of the present invention is directed to a toner comprising particles of a resin and an optional colorant, said toner particles having coated thereon a polypyrrole. Another embodiment of the present invention is directed to a process which comprises (a) generating an electrostatic latent image on an imaging member, and (b) developing the latent image by contacting the imaging member with charged toner particles comprising a resin and an optional colorant, said toner particles having coated thereon a polypyrrole.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrophotographic imaging process, as taught by C. F. Carlson in U.S. Pat. No. 2,297,691, entails placing a uniform electrostatic charge on a photoconductive insulating layer known as a photoconductor or photoreceptor, exposing the photoreceptor to a light and shadow image to dissipate the charge on the areas of the photoreceptor exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material known as toner. Toner typically comprises a resin and a colorant. The toner will normally be attracted to those areas of the photoreceptor which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This developed image may then be transferred to a substrate such as paper. The transferred image may subsequently be permanently affixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
Another known process for forming electrostatic images is ionography. In ionographic imaging processes, a latent image is formed on a dielectric image receptor or electroreceptor by ion or electron deposition, as described, for example, in U.S. Pat. Nos. 3,564,556, 3,611,419, 4,240,084, 4,569,584, 2,919,171, 4,524,371, 4,619,515, 4,463,363, 4,254,424, 4,538,163, 4,409,604, 4,408,214, 4,365,549, 4,267,556, 4,160,257, and 4,155,093, the disclosures of each of which are totally incorporated herein by reference. Generally, the process entails application of charge in an image pattern with an ionographic or electron beam writing head to a dielectric receiver that retains the charged image. The image is subsequently developed with a developer capable of developing charge images.
Many methods are known for applying the electroscopic particles to the electrostatic latent image to be developed. One development method, disclosed in U.S. Pat. No. 2,618,552, the disclosure of which is totally incorporated herein by reference, is known as cascade development. Another technique for developing electrostatic images is the magnetic brush process, disclosed in U.S. Pat. No. 2,874,063. This method entails the carrying of a developer material containing toner and magnetic carrier particles by a magnet. The magnetic field of the magnet causes alignment of the magnetic carriers in a brushlike configuration, and this xe2x80x9cmagnetic brushxe2x80x9d is brought into contact with the electrostatic image bearing surface of the photoreceptor. The toner particles are drawn from the brush to the electrostatic image by electrostatic attraction to the undischarged areas of the photoreceptor, and development of the image results. Other techniques, such as touchdown development, powder cloud development, and jumping development are known to be suitable for developing electrostatic latent images.
Powder development systems normally fall into two classes: two component, in which the developer material comprises magnetic carrier granules having toner particles adhering triboelectrically thereto, and single component, which typically uses toner only. Toner particles are attracted to the latent image, forming a toner powder image. The operating latitude of a powder xerographic development system is determined to a great degree by the ease with which toner particles are supplied to an electrostatic image. Placing charge on the particles, to enable movement and imagewise development via electric fields, is most often accomplished with triboelectricity.
The electrostatic image in electrophotographic copying/printing systems is typically developed with a nonmagnetic, insulative toner that is charged by the phenomenon of triboelectricity. The triboelectric charging is obtained either by mixing the toner with larger carrier beads in a two component development system or by rubbing the toner between a blade and donor roll in a single component system.
Triboelectricity is often not well understood and is often unpredictable because of a strong materials sensitivity. For example, the materials sensitivity causes difficulties in identifying a triboelectrically compatible set of color toners that can be blended for custom colors. Furthermore, to enable xe2x80x9coffsetxe2x80x9d print quality with powder-based electrophotographic development systems, small toner particles (about 5 micron diameter) are desired. Although the functionality of small, triboelectrically charged toner has been demonstrated, concerns remain regarding the long-term stability and reliability of such systems.
In addition, development systems which use triboelectricity to charge toner, whether they be two component (toner and carrier) or single component (toner only), tend to exhibit nonuniform distribution of charges on the surfaces of the toner particles. This nonuniform charge distribution results in high electrostatic adhesion because of localized high surface charge densities on the particles. Toner adhesion, especially in the development step, can limit performance by hindering toner release. As the toner particle size is reduced to enable higher image quality, the charge Q on a triboelectrically charged particle, and thus the removal force (F=QE) acting on the particle due to the development electric field E, will drop roughly in proportion to the particle surface area. On the other hand, the electrostatic adhesion forces for tribo-charged toner, which are dominated by charged regions on the particle at or near its points of contact with a surface, do not decrease as rapidly with decreasing size. This so-called xe2x80x9ccharge patchxe2x80x9d effect makes smaller, triboelectric charged particles much more difficult to develop and control.
To circumvent limitations associated with development systems based on triboelectrically charged toner, a non-tribo toner charging system can be desirable to enable a more stable development system with greater toner materials latitude. Conventional single component development (SCD) systems based on induction charging employ a magnetic loaded toner to suppress background deposition. If with such SCD systems one attempts to suppress background deposition by using an electric field of polarity opposite to that of the image electric field (as practiced with electrophotographic systems that use a triboelectric toner charging development system), toner of opposite polarity to the image toner will be induction charged and deposited in the background regions. To circumvent this problem, the electric field in the background regions is generally set to near zero. To prevent deposition of uncharged toner in the background regions, a magnetic material is included in the toner so that a magnetic force can be applied by the incorporation of magnets inside the development roll. This type of SCD system is frequently employed in printing apparatus that also include a transfuse process, since conductive (black) toner may not be efficiently transferred to paper with an electrostatic force if the relative humidity is high. Some printing apparatus that use an electron beam to form an electrostatic image on an electroreceptor also use a SCD system with conductive, magnetic (black) toner. For these apparatus, the toner is fixed to the paper with a cold high-pressure system. Unfortunately, the magnetic material in the toner for these printing systems precludes bright colors.
Powder-based toning systems are desirable because they circumvent a need to manage and dispose of liquid vehicles used in several printing technologies including offset, thermal ink jet, liquid ink development, and the like. Although phase change inks do not have the liquid management and disposal issue, the preference that the ink have a sharp viscosity dependence on temperature can compromise the mechanical properties of the ink binder material when compared to heat/pressure fused powder toner images.
To achieve a document appearance comparable to that obtainable with offset printing, thin images are desired. Thin images can be achieved with a monolayer of small (about 5 micron) toner particles. With this toner particle size, images of desirable thinness can best be obtained with monolayer to sub-monolayer toner coverage. For low micro-noise images with sub-monolayer coverage, the toner preferably is in a nearly ordered array on a microscopic scale.
To date, no magnetic material has been formulated that does not have at least some unwanted light absorption. Consequently, a nonmagnetic toner is desirable to achieve the best color gamut in color imaging applications.
For a printing process using an induction toner charging mechanism, the toner should have a certain degree of conductivity. Induction charged conductive toner, however, can be difficult to transfer efficiently to paper by an electrostatic force if the relative humidity is high. Accordingly, it is generally preferred for the toner to be rheologically transferred to the (heated) paper.
A marking process that enables high-speed printing also has considerable value.
Electrically conductive toner particles are also useful in imaging processes such as those described in, for example, U.S. Pat. Nos. 3,639,245, 3,563,734, European Patent 0,441,426, French Patent 1,456,993, and United Kingdom Patent 1,406,983, the disclosures of each of which are totally incorporated herein by reference.
U.S. Pat. No. 5,834,080 (Mort et al.), the disclosure of which is totally incorporated herein by reference, discloses controllably conductive polymer compositions that may be used in electrophotographic imaging developing systems, such as scavengeless or hybrid scavengeless systems or liquid image development systems. The conductive polymer compositions includes a charge-transporting material (particularly a charge-transporting, thiophene-containing polymer or an inert elastomeric polymer, such as a butadiene- or isoprene-based copolymer or an aromatic polyether-based polyurethane elastomer, that additionally comprises charge transport molecules) and a dopant capable of accepting electrons from the charge-transporting material. The invention also relates to an electrophotographic printing machine, a developing apparatus, and a coated transport member, an intermediate transfer belt, and a hybrid compliant photoreceptor comprising a composition of the invention.
U.S. Pat. No. 5,853,906 (Hsieh), the disclosure of which is totally incorporated herein by reference, discloses a conductive coating comprising an oxidized oligomer salt, a charge transport component, and a polymer binder, for example, a conductive coating comprising an oxidized tetratolyidiamine salt of the formula 
a charge transport component, and a polymer binder, wherein Xxe2x88x92 is a monovalent anion.
U.S. Pat. No. 5,457,001 (Van Ritter), the disclosure of which is totally incorporated herein by reference, discloses an electrically conductive toner powder, the separate particles of which contain thermoplastic resin, additives conventional in toner powders, such as coloring constituents and possibly magnetically attractable material, and an electrically conductive protonized polyaniline complex, the protonized polyaniline complex preferably having an electrical conductivity of at least 1 S/cm, the conductive complex being distributed over the volume of the toner particles or present in a polymer-matrix at the surface of the toner particles.
U.S. Pat. No. 5,202,211 (Vercoulen et al.), the disclosure of which is totally incorporated herein by reference, discloses a toner powder comprising toner particles which carry on their surface and/or in an edge zone close to the surface fine particles of electrically conductive material consisting of fluorine-doped tin oxide. The fluorine-doped tin oxide particles have a primary particle size of less than 0.2 micron and a specific electrical resistance of at most 50 ohms.meter. The fluorine content of the tin oxide is less than 10 percent by weight, and preferably is from 1 to 5 percent by weight.
U.S. Pat. No. 5,035,926 (Jonas et al.), the disclosure of which is totally incorporated herein by reference, discloses new polythiophenes containing structural units of the formula 
in which A denotes an optionally substituted C1-C4 alkylene radical, their preparation by oxidative polymerization of the corresponding thiophenes, and the use of the polythiophenes for imparting antistatic properties on substrates which only conduct electrical current poorly or not at all, in particular on plastic mouldings, and as electrode material for rechargeable batteries.
While known compositions and processes are suitable for their intended purposes, a need remains for improved marking processes. In addition, a need remains for improved electrostatic imaging processes. Further, a need remains for toners that can be charged inductively and used to develop electrostatic latent images. Additionally, a need remains for toners that can be used to develop electrostatic latent images without the need for triboelectric charging of the toner with a carrier. There is also a need for toners that are sufficiently conductive to be employed in an inductive charging process without being magnetic. In addition, there is a need for conductive, nonmagnetic toners that enable controlled, stable, and predictable inductive charging. Further, there is a need for conductive, nonmagnetic, inductively chargeable toners that are available in a wide variety of colors. Additionally, there is a need for conductive, nonmagnetic, inductively chargeable toners that enable uniform development of electrostatic images. A need also remains for conductive, nonmagnetic, inductively chargeable toners that enable development of high quality full color and custom or highlight color images. In addition, a need remains for conductive, nonmagnetic, inductively chargeable toners that enable generation of transparent, light-transmissive color images. Further, a need remains for toners suitable for use in printing apparatus that employ electron beam imaging processes. Additionally, a need remains for toners suitable for use in printing apparatus that employ single component development imaging processes. There is also a need for conductive, nonmagnetic, inductively chargeable toners that can be prepared by relatively simple and inexpensive methods. In addition, there is a need for conductive, nonmagnetic, inductively chargeable toners wherein the toner comprises a resin particle encapsulated with a conductive polymer, wherein the conductive polymer is chemically bound to the particle surface. Further, there is a need for insulative, triboelectrically chargeable toners that are available in a wide variety of colors. Additionally, there is a need for insulative, triboelectrically chargeable toners that enable uniform development of electrostatic images. There is also a need for insulative, triboelectrically chargeable toners that enable development of high quality full color and custom or highlight color images. In addition, there is a need for insulative, triboelectrically chargeable toners that enable generation of transparent, light-transmissive color images. Further, there is a need for insulative, triboelectrically chargeable toners that can be prepared by relatively simple and inexpensive methods. Additionally, there is a need for insulative, triboelectrically chargeable toners wherein the toner comprises a resin particle encapsulated with a polymer, wherein the polymer is chemically bound to the particle surface. A need also remains for insulative, triboelectrically chargeable toners that can be made to charge either positively or negatively, as desired, without varying the resin or colorant comprising the toner particles. In addition, a need remains for insulative, triboelectrically chargeable toners that can be made to charge either positively or negatively, as desired, without the need to use or vary surface additives. Further, a need remains for both conductive, inductively chargeable toners and insulative, triboelectrically chargeable toners that enable production of toners of different colors that can reach the same equilibrium levels of charge, and that enable modification of toner color without affecting the charge of the toner; the sets of different colored toners thus prepared enable generation of high quality and uniform color images in color imaging processes.
The present invention is directed to a toner comprising particles of a resin and an optional colorant, said toner particles having coated thereon a polypyrrole. Another embodiment of the present invention is directed to a process which comprises (a) generating an electrostatic latent image on an imaging member, and (b) developing the latent image by contacting the imaging member with charged toner particles comprising a resin and an optional colorant, said toner particles having coated thereon a polypyrrole.